1. Field of the Disclosure
The present disclosure relates generally to an electrostatographic printing apparatus, and more particularly, concerns externally heating a photoreceptor used in such a machine.
2. Description of Related Art
Typically, in an electrostatographic printing process of printers, a photoconductive or photoreceptor member is charged by a charging device to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoreceptor member is exposed to selectively dissipate the charges thereon in the irradiated areas. This records an electrostatic latent image on the photoreceptor member. After the electrostatic latent image is recorded on the photoreceptor member, the latent image is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules either to a donor roll or to a latent image on the photoreceptor member. The toner attracted to the donor roll is then deposited on latent electrostatic images on a charge retentive surface, which is usually a photoreceptor. The toner powder image is then transferred from the photoreceptor member to a copy substrate.
In order to fix or fuse the toner material onto a support member permanently by heat, it is necessary to elevate the temperature of the toner material to a point at which constituents of the toner material coalesce and become tacky. This action causes the toner to flow, to some extent, onto fibers or pores of the support members or otherwise upon surfaces thereof. Thereafter, as the toner materials cool, solidification of the toner materials occurs causing the toner material to be bonded firmly to the support member.
Transfer is typically carried out by the creation of a “transfer-detack zone” (often abbreviated to just “transfer zone”) of AC and DC biases where the print sheet is in contact with, or otherwise proximate to, the photoreceptor member. A DC bias applied to the back (i.e., on the face away from the photoreceptor member) of the paper or other substrate in the transfer zone electrostatically transfers the toner from the photoreceptor member to the paper or other substrate presented to the transfer zone. The toner particles are heated to permanently affix the powder image to the copy substrate. Biased transfer rolls are also used to transfer an image from a photoreceptor member to media, for example, the segmented bias roll disclosed in U.S. Pat. No. 3,847,478.
In high humidity environments, such as, greater than 70% relative humidity, a problem is sometimes encountered in some machines when certain ionic species generated by corona combine with moisture on the photoreceptor surface to form conductive paths. The surface charge corresponding to the electrostatic latent image moves. This distorts the integrity of the latent image. The result is observed as image blur. Aggressively refreshing the photoreceptor surface (high wear rates typically in the range of 20 to 100 nm/k cycle) is the usual method used to avoid this problem. Well known in the art is the use of drum heaters that usually reside inside the photoreceptor drum to reduce surface moisture as shown, for example, in U.S. Pat. Nos. 4,161,357; 5,019,682; and 7,599,642 B2. Other techniques for controlling moisture on a photoreceptor are related to the addition of material additives in the photoreceptor composition to reduce this effect. Additionally, air circulation around the charging devices or the use of expensive coatings on charge devices has been tried. These traditional fixes have related drawbacks of added expense, additional power consumption, low photoreceptor life, or limitations on operating environment.
Thus, there is still a need for a method for controlling moisture on the surface of a photoreceptor that is inexpensive, low in power consumption and is not detrimental to the life of the photoreceptor.